Primary Defences In Humans

Question 1

Skin

Answer 1

Main primary defence

Outer layer = epidermis (layers of cells). Most of these cells are keratinocytes (produced at base by mitosis then migrate to surface). As they migrate, cytoplasm dries out and is replaced by protein keratin

When cells reach surface they are dead. Layer of dead cells = barrier to pathogens

Question 2

Blood clotting

Answer 2

Involves calcium ions and 12 clothing factors

Clotting factors released from platelets and damaged tissue - activate enzyme cascade

Question 3

Blood clot timeline (pink - main points)

Answer 3

Damage to tissue exposes collagen and releases clotting factors -> platelets bind to collagen and release clotting factors -> temporary plug of platelets -> scab -> red blood cells trapped

Question 4

Blood clot timeline (green - enzymes )

Answer 4

1. Inactive thrombokinase -> active thrombokinase (enzyme)
2. Active thrombokinase + prothrombin in blood + Ca2+ -> active thrombin
3. Active thrombin + soluble fibrinogen in plasma -> insoluble fibrin
4. Fibres attach to platelets in plug -> clot

Question 5

Skin repair

Answer 5

Deposition of fibrous collagen under scab

Stem cells in epidermis divide by mitosis to form new cells which migrate to edges of cut and differentiate to form new skin

New blood vessels grow

Tissues contract to help draw edges of cut together

As new skin is completed, scab is released